Fuel cells, which generate electricity through an electrochemical reaction of a fuel gas and an oxidant gas, are a notable energy source. A so-called reforming type fuel cell system is one type of fuel cell system furnished with such a fuel cell. A reforming type fuel cell system (herein termed simply “a fuel cell system”) is a fuel cell system of a type in which a feedstock (such as an alcohol, hydrocarbon, aldehyde, or the like) is reformed by a reformer to generate a reformed gas, and the fuel gas (hydrogen) contained in this reformed gas is utilized by the fuel cell to generate electricity.
In such fuel cell systems, a steam reforming reaction, which affords excellent hydrogen yield, is often employed to reform the fuel in the reformer. Also, the steam reforming reaction is an endothermic reaction. Thus, in order to maintain the proper reaction temperature, the reformer is typically heated by a burner. Moreover, in such fuel cell systems, it is common practice for fuel gas not consumed by electricity generation in the fuel cell to be combusted in the burner, for the purpose of efficiently utilizing the fuel gas generated by the reformer.
In the fuel cell systems described above, generating a prescribed quantity of fuel gas requires controlling the feed rate of feedstock and or steam to the reformer, as well as controlling the temperature of the reformer, i.e. combustion in the combustion section. The reason is that reforming efficiency (the conversion rate in the reforming reaction) is closely related to the temperature of the reformer. Accordingly, for conventional fuel cell systems, a number of techniques have been proposed for controlling combustion in the combustion section on the basis of various sensor readings, in order to maintain appropriate reforming efficiency levels and improve generation efficiency in the fuel cells.
Patent Citation 1: JP-A 2000-34101
Patent Citation 2: JP-A 2004-60910
Patent Citation 3: JP-A 2005-26059
Patent Citation 4: JP-A 2006-331990